The present invention relates in general to internal combustion engines, and more particularly to the control of fuel injection and ignition timing in an internal combustion engine operating on a fuel mixture of gasoline and methanol.
In an effort to protect the environment and conserve fuel sources, efforts have been made to improve the efficiency of operation of internal combustion engines. However, recent regulations which are directed to reduction of NO in exhaust gas seem to require measures which tend to conflict with efficient engine operation, since increase in efficiency of engine operation tends to result in an increase in NO in the exhaust gas.
It is known that, to decrease NO in the exhaust gas of an internal combustion engine, it is necessary only to maintain the maximum temperature of cylinder combustion to less than 1600.degree. C. The two ways of improving heat efficiency are to lower exhaust gas heat and reduce engine friction.
One easy method to address this problem is to use an EGR (exhaust gas recycle) method, which is a known way to reduce NO in exhaust gas. However, the EGR method has several drawbacks, including an increase in the HC and CO levels in the exhaust gas, as well as contamination of the injection port with dust carried in the EGR gas.
Another method of reducing NO in the exhaust gas of an internal combustion engine is to use an alternative fuel, such as methanol mixed gasoline. In this regard, because of its chemical nature, methanol has a lower combustion temperature than gasoline. Thus, using a methanol-gasoline mixture provides for a reduced temperature of cylinder combustion and a consequent reduction in NO in the exhaust gas, but without increasing the levels of HC and CO, as occurs in EGR systems.
Much experimentation has been directed to the use of methanol mixed gasoline in conventional internal combustion engines, but major problems still block the widespread use of this alternative fuel. One of these problems relates to the fact that it is very difficult to start an engine on a methanol-gasoline mixture when the temperature is below 45.degree. F. One proposed solution to the cold-starting problem involves the use of gasoline from an auxiliary tank during starting and warm-up, with a switch being made to the methanol-gas mixture after the engine is warmed up. However, this solution is too costly and ineffective in controlling emissions.
Another problem with the use of methanol mixed gasoline is the difficulty in obtaining maximum torque during warm-up. Known engine control systems for methanol engines control the ignition timing on the basis of the detected methanol-gasoline mixture being burned, but no attention has been given to the need to also control the fuel injection volume to achieve maximum torque, depending on the methanol-gasoline mixture.